This invention relates generally to sensors for detecting analytes in fluids. More particularly, it relates to an array of sensors useful for constructing xe2x80x9celectronic nosesxe2x80x9d for analyzing complex vapors and producing a sample output.
There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (1-2). This system is thought to utilize probabilistic repertoires of many different receptors to recognize a single odorant (3-4). In such a configuration, the burden of recognition is not on highly specific receptors, as in the traditional xe2x80x9clock-and-keyxe2x80x9d molecular recognition approach to chemical sensing, but lies instead on the distributed pattern processing of the olfactory bulb and the brain (5-6).
Prior attempts to produce a broadly responsive sensor array have exploited heated metal oxide thin film resistors (7-9), polymer sorption layers on the surfaces of acoustic wave resonators (10-11), arrays of electrochemical detectors (12-14), or conductive polymers (15-16). Arrays of metal oxide thin film resistors, typically based on SnO2 films that have been coated with various catalysts, yield distinct, diagnostic responses for several vapors (7-9). However, due to the lack of understanding of catalyst function, SnO2 arrays do not allow deliberate chemical control of the response of elements in the arrays nor reproducibility of response from array to array. Surface acoustic wave resonators are extremely sensitive to both mass and acoustic impedance changes of the coatings in array elements, but the signal transduction mechanism involves somewhat complicated electronics, requiring frequency measurement to 1 Hz while sustaining a 100 MHz Rayleigh wave in the crystal (10-11). Attempts have also been made to construct sensors with conducting polymer elements that have been grown electrochemically through nominally identical polymer films and coatings (15-18). Moreover, Pearce et al., (1993) Analyst 118:371-377, and Gardner et al., (1994) Sensors and Actuators B 18-19:240-243 describe, polypyrrole-based sensor arrays for monitoring beer flavor. Shurmer (1990) U.S. Pat. No. 4,907,441, describes general sensor arrays with particular electrical circuitry.
Although the foregoing systems have some usefulness, these still remains a need in the art for a low cost, broadly responsive analyte detection sensor array based on a variety of sensors. The present invention fulfills this and other needs.
The present invention relates to a device for detecting a chemical analyte in a fluid, which includes gases, vapors and liquids. As such, the present invention relates to a device for detecting a chemical analyte, comprising: a sensor array connected to a measuring apparatus having at least one sensor comprising regions of nonconductive material and conductive material compositionally different than the nonconductive material, wherein the conductive material comprises a nanoparticle; and a response path through the regions of nonconductive material and the conductive material. In certain aspects, the sensor array is based on a variety of xe2x80x9cchemiresistorxe2x80x9d elements. Such elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. In addition, these sensors yield a rapid, low power signal in response to an analyte of interest, and their signals are readily integrated with software or hardware-based neural networks. The signal output can be in the form of resistance, impedance, capacitance, optics, fluorescence or other means useful for purposes of analyte identification.
In certain aspects, device includes a substrate having at least one surface and at least two sensors fabricated onto the surface, wherein each sensor has a first and second electrical lead which are electrically connected to a chemically sensitive resistor. The resistor comprises a plurality of alternating nonconductive regions (comprising a nonconductive organic material) and conductive regions (comprising a conductive material or particle). The electrical path between the first and second leads is transverse to (i.e., passes through) the plurality of alternating nonconductive and conductive regions. In use, the resistor provides a difference in resistance between the conductive elements when 1) contacted with a fluid comprising a chemical analyte at a first concentration, than when contacted with a fluid comprising the chemical analyte at a second different concentration or 2) contacted with a fluid comprising a first chemical analyte at a concentration, than when contacted with a fluid comprising a second chemical analyte (different from the first) at the same concentration.
The variability in chemical sensitivity from sensor to sensor is conveniently provided by qualitatively or quantitatively varying the composition of the conductive and/or nonconductive regions. For example, in one embodiment, the conductive material in each resistor is held constant (e.g., the same conductive material such as polypyrrole, or carbon black), while the nonconductive material varies between resistors (e.g., different polymers).
In another embodiment, the conductive material is a conductive particle, such as a nanoparticle. In certain embodiments, the alternating nonconductive regions can be a covalently attached ligand to a conductive core (the conductive region). These ligands can be polyhomo- or polyheterofunctionalized, thereby being suitable for the detection of various analytes. Arrays of such sensors are constructed with at least two sensors having different chemically sensitive resistors providing various differences in resistance. An electronic nose for detecting an analyte in a fluid can be constructed by using such arrays in conjunction with an electrical measuring device electrically connected to the conductive elements of each sensor. Such electronic noses can incorporate a variety of additional components, including means for monitoring the temporal response of each sensor, assembling and analyzing sensor data to determine analyte identity, analyte concentration, or quality control determinations. Methods of making and using the disclosed sensors, arrays and electronic noses are also provided.